Monofuel propellant booster rocket



Oct. '1, 1963 -MoNoFuEL 1v=Ro1=ELmmTl BOOSTER ROCKET Filed Feb." 2e, 1959 'Lr/ ze 17.1221' Hans f/ce/reryer H. P.' EicHNBERGER 3,105,350' l l@ Patented ct. l, 1953 3,105,350 MNQFUEL PROPELLANT BSTER ROCKET Hans P. Eiclieuberger, Cleveland, Unio, assigner to Thompson Ramo Wooldridge Ine., Cleveland, laio, a corporation of Ohio Filed Feb. Z6, 1959, Ser. No. 795,751 2 Claims. (Cl. S0-35.3)

This invention relates to gas generating apparatus of the type adapted to produce a large quantity of gas in a relatively short interval of time. More particularly, this invention relates to a booster-type rocket engine adapted to burn a gelatinous mono-propellant in such a manner as to produce high thrust per unit cross-sectional area of the rocket engine.

It is a feature of the present invention to provide a high thrust, short duration booster type rocket engine which may conveniently comprise a long narrow container or elongated fuel tank having a thrust producing gas discharge nozzle in open communication with one end thereof. Packed inside the fuel tank is a body of gelatinous mono-propellant defining a plurality of longitudinal passages therein. Where it is desired to provide simply a booster type rocket in which no in-ight variable control of the burning rate is desired, the passages may be entirely filled with bars or rods of a high burning rate solid fuel or propellant. When lthese rods of solid propellant are ignited they burn themselves out rapidly leaving the open passages in the body of gelatinous monopropellant and simultaneously igniting the surfaces of the gelatinous mono-propellant defining walls of the passage. It is Ithus possible to burn all or substantially all of the gelatinous mono-propellant in the container without extruding the said mono-propellant into a combustion chamber as has heretofore been the usual practice Where it is desired to provide a similar rocket engine in which some control of the burning rate in flight is desired, the solid fuel may extend only slightly into the passages to act as an initial igm'ting means and the rest of the passages may be filled with a liquid such as Water, ammonia, or any other non-combustible lfluid which is held under a controlled pressure in the passages by a piston arrangement. When the solid fuel has burned the liquid will be pushed backwardly in the passages by the combustion chamber pressure and will be urged forwardly in the passages by pressure applied by the piston. Consequently, the position of the liquid in the passages can be controlled by varying the equilibrium position of these two forces. The operation of this embodiment of the invention depends on the fact that the burning rate of solid or a gelatinous mono-propellant composition depends upon the rate of heat transfer and upon the chemical equilibrium at the burning face. By placing the liquid in contact with the burning face, the burning rate of the monopropellant may therefore be controlled. Preferably, of course, the liquid should be one having a high chemical heat of evaporation and one which upsets the chemical equilibrium at the burning face.

In either embodiment both solid and gelatinous monopropellants can be used as the main body of thrust producing fuel. Gelatinous thrust producing compositions which have recently been developed, although less rigid than solid fuels, nonetheless do otherwise combine many of the advantages and eliminate many of the disadvantages of the more commonly used solid and liquid propellants. Used in a rocket engine of the type described above they are Well adapted to obtain high thrusts per unit frontal area Without resorting to an internal burning solid fuel rocket which is subject to grain cracking and other characteristics which require site loading and which pose other well-known logistic problems.

-It is therefore an object of this invention to provide a novel booster type rocket engine.

It is a further object of this invention to provide gas generating apparatus particularly adapted for producing large quantities of gas during a relatively short time interval.

It is a further object of this invention to provide a gelatinous mono-propellant fueled rocket engine wherein a body of said fuel defines longitudinal passages therein within a fuel tank which is also adapted to serve as a combustion chamber when said fuel is ignited to burn along said passages.

It is a further object of this invention to provide such a rocket engine wherein the rate of burning of 4the fuel may be controlled by controlling the position of an inert liquid in said passages.

Other objects, features, and advantages of the present invention will be more fully apparent to those skilled in the art from the following detailed description taken in connection -with the accompanying drawings in which like reference characters refer to like parts throughout and wherein: y

FIGURE l is a longitudinal sectional view of a booster type rocket engine in accordance with the present invention.

FIGURE 2 is a transverse sectional view taken along line II-II of FIGURE l.

FIGURE 3 is a longitudinal sectional view of a rocket engine in accordance with a second embodiment of the invention.

Liquid and solid propellants or fuels suitable for use in rocket engines have been widely known in the art for some time. More recently, gelatinous propellants, and more particularly, gelatinous mono-propellants, have been developed which combine many of the advantages and eliminate many of the disadvantages of solid and liquid fuels. In general, the type of mono-propellant compositions suitable for use in the present invention is a relatively sti or non-fluid gelatinous material. Such a relatively stiff gelatinous material may be formed by increasing the polymer content of gelatinous mono-propellant compositions heretofore used in burning apparatus wherein such compositions were given a more viscous consistency in order that they be readily extrudable from a fuel tank into a combustion chamber.

Numerous suitable mono-propellant mixtures can be made into either the extrudable or the stiffer shape deiining form. Such mixtures preferably comprise a stable dispersion of a finely divided, insoluble solid oxidizer in a continuous matrix of an oxidizable liquid fuel. The liquid fuel can be any oxidizable liquid, preferably an organic liquid containing carbon and hydrogen. Such liquid fuels include hydrocarbons such as triethyl benzene, dodecane and the like; compounds containing oxygen linked to a carbon atom such as esters including methyl maleate, diethyl phthalate, butyl oxalate, and the like; alcohols such as benzyl alcohol, triethylene glycol and the like; ethers such as methyl o-naphthyl ether and the like, and many others.

The solid oxidizer can be any suitable, active oxidizing agent which yields `an oxidizing element such as oxygen, chlorine or fluorine readily for combustion of the fuel and which is insoluble in the liquid fuel vehicle. Such oxidizers include inorganic `oxidizing salts such as ammonia, sodium and potassium perchlorate or nitrate and the metal peroxides such as barium peroxide.

Finely divided solid metal powders such as aluminum or magnesium may be incorporated in the mono-propellant composition as an additional fuel component along With the liquid fuel. Such metal powders possess the advantages both of increasing the fuel density and improv- 3 ing the specific impulse of the mono-propellant because of their high heats of combustion.

Gelling agents for imparting the desired cohesiveness and iow characteristics to the plastic mixture include natural and synthetic polymers such as polyvinyl chloride, polyvinyl acetate, cellulose esters such as cellulose acetate, cellulose ethers such as ethyl cellulose, metal salts of higher fatty acids such as the sodium or magnesium stearates and palmitates.

The amount of oxidizer is prefer-ably at a stoichiometric level with respect to the liquid fuel, although minimum concentrations of solid `oxidizer as low as 40% by weight are operative. In general, the oxidizer will constitute about 65% by weight of the mixture. A preferred operative mono-propellant includes a gel composed of up to 50% by weight of a liquid fuel, from 40i to 65% by weight of an oxidizer and from 3 to 10% by weight of a gelling agent. A specific operative fuel can be composed of about 48% by weight of solid oxidizers such as potassium perchlorate, about 42% by weight `of liquid fuel such as triethyl benzine, and about by weight of a gelling agent such as ethyl cellulose. It is to be understood, however, that this invention is not limited to use with any particular gelatinous mono-propellant mixture or indeed to any particular solid propellant, but rather it is directed to the principles of a novel gas generating apparatus such as a rocket engine using any suitable fuel.

One embodiment of a high thrust booster type rocket in accordance with the present invention is shown in FIG- URE 1 and comprises an elongated fuel tank 10 which is preferably generally cylindrical in shape and of considerable length to diameter ratio (the showing in FIG- URE 1 not being drawn to scale). Disposed within the tank 10 is a body 11 of gelatinous mono-propellant thrust producing composition of the type described in detail above. The body 11 of gelatinous thrust producing composition defines therein a plurality of longitudinally extending passages 12. Preferably these passages extend coaxially with the axis of the cylindrical tank 10 and hence in parallel relationship to each other throughout the length of the body of fuel 11.

Disposed within the passages 12 are rods 13 of a rapidly burning solid propellant material. The particular solid propellant used may be any high energy solid propellant having a high burning rate. Many such propellants are known to the art. Such high energy solid propellants include for example those of the perchlorate family and those from the nitrocellulose or nitroglycerine families.

The solid propellant rods 13` are snugly received within the passages 12 so that their outer surface is in contact with the inner surface of gelatinous monopropellant defining the walls of the passages 12. rThe diameter of the rods 13 and hence the diameter of the passages 12, is not critical but may be varied to suit the needs of any particular application. In particular, the rods 13` may have a diameter ranging from a few thousandths of an inch up to one-quarter or one-half inch. Similarly, the spacing between the rods 13 and hence the number of rods used in any given rocket is also not critical but may be varied to suit the thrust generating needs of any particular application.

Each of the solid propellant rods 13 terminates at the rearward portion of the fuel tank 10 in contact with a circular plate 14 of the same solid propellant to which the rod 13 may be attached in any convenient manner as by cement or any other adhesive means. The plate 14 is positioned in close proximity to any conventional igniting means 15 which may be actuated from a battery or other voltage source 16. The igniter 15 may, for example, be of the hot wire type which ignites the plate 14 when the switch 17 is closed. Ignition of the plate 14 of solid propellant in turn ignites each of the rods 13 which are in contact therewith.

In operation, the plate 14 of solid propellant when ignited burns rapidly and ignites each of the rods 13. The high burning rate solid propellant rods rapidly burn away from the rearward portion of the fuel tank 10 toward the forward portion thereof, thereby leaving the passages 12 empty and igniting the gelatinous mono-propellant 11 surrounding each of these passages. Each of the passages 12 thus becomes a small combustion charnber within the fuel tank proper. The fuel burns throughout the entire tank 10 and discharges gases rearwardly to ultimately be discharged to the nozzle 18 to generate thrust.

As noted above, the arrangement shown in FIGURE 1 avoids the necessity of providing means to extrude the gelatinous mono-propellant into a combustion chamber as has heretofore been the practice while at the same time retaining the desirable features which have been found to result from the use of gelatinous mono-propellants. In particular, the use of gelatinous mono-propellants permits loading of a rocket such as shown in FIGURE 1 at the point of manufacture without danger of cracking of the propellant during shipment or ground handling thereof. The plate 14 of solid propellant in addition to acting as a part of the ignition system also acts as a vapor seal and retaining means during such ground handling. Cf course it will be understood that the use of such a plate is not essential to the invention since other means could be provided to individually ignite the rods 13 and other vapor seals and retaining means could easily be provided if desired. Further, as noted above, a relatively slow burning solid fuel could be used instead of the gelatinous fuel if desired.

With the structure shown in FIGURE 1, it is of course possible to establish a predetermined program of thrust generation by properly choosing the dimensions of the fuel tank and nozzle, the particular gelatinous mono-propellant, the particular solid propellant, and the relative dimensions and spacings of the solid propellant rods 13. Once such a predetermined thrust generation program has been so established, however, it is not possible with the system shown in FIGURE 1 to variably control the thrust generation. Once ignited, the booster type rocket shown in FIGURE 1 simply continues to burn and generates a relatively high thrust for a relatively short period of time at a rate and in a manner determined by the above noted dimensions and characteristics of the particular structure.

Where it is desired to provide some `degree of control in order to modulate the burning rate and hence the thrust generation rate of the rocket, an arrangement such as shown in FIGURE 3 may be used. In FIGURE 3, those parts corresponding to parts already discussed in connection with FIGURE 1 are indicated by the same reference character and will not be further discussed. In FIGURE 37 it will be noted that the rods of solid propellant 13a are merely parts of the ignition system associated with the plate 14 and do no-t extend the full length of the passages 12. The rods 13a extend only sufficiently far into the pass-ages -12 to start ignition of the fuel around the side walls of the rearward portions of these passages. The remainder of the passages 12 is initially filled with liquid 19 such as water, ammonia, or the like. During ground handling the plate 14 and stub rods 13a seal this liquid from escaping from the rearward portion ofthe passages whereas a piston Z0 slidably `mounted in the forward portion of ythe fuel tank 10 seals the liquid 19 from the forward end. Piston 20 may be actuated for `sliding motion backward and forward in vthe fuel tank 10` by an actuating member Z1 which :may in turn be driven by any conventional suitable mechanical, pneumatic or hydraulic means.

When the piston 20 is in the position shown in FIG- URE 3, the liquid 19 occupies the complete length of all of the passages 12 and is urged against the rods 13a. When the switch 17 is closed thereby igniting the plate 14 and the rod 13a, pressure is built up in `the rearward portion of the fuel tank which acts against the surface of the liquid 19 thereby tending to urge it forwardly in the lfuel tank 10 against the action of the piston 20. Of course, if this pressure exceeds the pressure applied by piston 20 the liquid 19 will be forced forwardly thereby permitting the fuel to continue to burn down into the passages 12. When the generated pressure thusV exceeds `the pressure applied to member 21, piston y21 slides forwardly in the tank 10 permitting the liquid 19 to escape into the forward reservoir and thereby emptying a portion of the passages 12 so that the burning surface of the mono-propellant is increased in area. This in turn increases the thrust generated. Hence, the pressure applied to the member 21 can afford a control over the thrust generated by the system. Y

It should be noted that although it is preferred to use a gelatinous mono-propellant in the arrangement shown in FIGURE 3, the mono-propellant composition 11' therein could also be a solid fuel. With either the solid 'or gelatinous thrust producing compositions, the burning rate of the composition to be controlled depends on the rate of heat transfer Iwithin the composition and on the chemical equilibrium established at the burning face of the Y composition. The thrust control in accordance with the embodiment in FIGURE A3 is achieved by placing a liquid such as water or ammonia in contact With the burning face. The liquid used should have a high chemical heat of evaporation and should be one which upsets the chemical equilibrium at this burning face. As noted above, retracting the piston in the forward portion of the tank permits ythe `chamber or tank pressure to urge the liquid forward in the holes or passages to .thereby accelerate the v burning rate of the thrust producing composition. Of

course, increasing the pres-sure applied to the piston .will afford greater resistance to the motion of the liquid and hence will decrease the burning rate of the thrust producing composition. In the arrangement shown, although it is possible to increase or deoreasetthe burning rate of the thrust producing composition, it is not intended that the rocket should be completely shut down and reignited.

While a particular exemplary preferred embodiment of the invention has been described in detail above, it will be understood that modifications and variations therein may be effected without departing from the true spirit and scope of the novel concepts of the present invention as defined 4by the following claims. n

I claim as my invention:

1. A method of generating gases comprising the steps of, embedding a rst mono-propellant of relatively fast burning rate in a second gelatinous mono-propellant of relatively slow burning rate and `of a lcohesive rigi-dness sufficient to permit the embedding of the first propellant therein, igniting the first mono-propellant to initially generate gases and to form passages the walls of which afford an extended internal burning surface area in the second mono-propellant after the first mono-.propellant has burned, and igniting the internal burning surface area of the second monoapropellant by the burning of the first mono-propellant to continue generation of gases.

2. A method `of operating a booster-type rocket engine to produce high thrust per unit cross-sectional area of the engine compising the steps of, embedding a solid propellant of relatively yfas-t burning rate in a gelatinous mono-propellant of relatively `slow burning rate, the gelatinous mono-propellant being contained within `the rocket engine and having a cohesive rigidness sufficient to permit embedding of the solid propellant therein, igniting the solid propellant to initially generate gases and yto thereby form at least one passage in the gelatinous mono-propellantthe walls of which afford an extended burning surface tarea of the gelatinous mono-propellant, and igniting the internal burning surface area of the gelatinous monopropellant by the burning of the solid propellant to continue the generation of gases.

References Cited in the file of this patent UNITED STATES PATENTS 1,880,579 Tilting Oct. 4, 1932 2,299,465 Coffman Oct. 20, 1942 2,434,652 Hickman Jan. 20, 1948 2,681,619 Chandler Iune 22, 1954 2,696,710 Golden Dec. 14, 1954 2,877,709 Duckworth Mar. 17, 1959 2,921,846 Noval Jan. 19, 1960 2,959,001 Porter Nov. 8, 1960 2,971,097 Corbett Feb. 7, 1961 2,988,877 Shope June 20, 1961 FOREIGN PATENTS 1,068,300 France Feb. 3, 1954 1,075,081 France Apr. 7, 1954 516,865 Great Britain Jan. 12, 1940 582,621 Great Britain Nov. 22, 1946 533,126 yItaly Sept. 19, 1955 

1. A METHOD OF GENERATING GASES COMPRISING THE STEPS OF, EMBEDDING A FIRST MONO-PROPELLANT OF RELATIVELY FAST BURNING RATE IN A SECOND GELATIOUS MONO-PROPELLANT OF RELATIVELY SLOW BURINING RATE AND OF A COHESSSIVE RIGIDNESS SUFFICIENT TO PERMIT THE EMBEDDING OF THE FIRST PROPELLANT THEREIN, IGNITING THE FIRST MONO-PROPELLANT TO INITIALLY GENERATE GASES AND TO FORM PASSAGES THE WALLS OF WHICH AFFORD AN EXTENDED INTERNAL BURNING SURFACE AREA IN THE SECOND MONO-PROPELLANT AFTER THE FIRST MONO-PROPELLANT 